Family Indriidae
indris, sifakas, and relatives

There are 11 species in 3 genera in the family Indriidae. The most diverse group are the sifakas (Propithecus), with 7 species. There are also 3 species of woolly lemurs (Avahi) and 1 species of indri (Indri). As in other lemuroid families, species diversity in Indriidae has increased substantially in recent years, going from 5 species recognized in 1991 to 11 in 2005. (Nowak, 1991; Wilson and Reeder, 2005)

Indriidae includes 5 recently extinct genera, representing 7 species. These species became extinct between 500 and 1,000 years ago. The extinctions of all of these species are thought to be directly related to environmental disruptions and hunting by humans soon after their immigration and expansion on Madagascar. (Nowak, 1991)

Indriids are endemic to Madagascar. (Mittermeier et al., 2006; Nowak, 1991; Tattersal, 1982; Wilson and Reeder, 2005)

Indriids are found in forests and scrublands throughout Madagascar. Species are found in rainforests and deciduous and evergreen forests, typically in forests with large, mature trees. (Mittermeier et al., 2006; Nowak, 1991; Tattersal, 1982)

The composition of Indriidae has remained relatively stable, although new species have been described in Avahi and Propithecus. Some researchers recognize up to 9 species of Propithecus. The genus Avahi was previously known as Lichanotus. Three subfamilies are sometimes recognized: Indriinae - with the three extant genera and the extinct genus Mesopropithecus, Archaeolemurinae - with the extinct genera Archaeolemur and Hadropithecus, and Palaeopithecinae - with the extinct genera Palaeopropithecus and Archaeoindris. (Nowak, 1991; Wilson and Reeder, 2005)

Indriids are morphologically diverse, from indris, the largest living strepsirhine species at up to 10 kg, to 1 kg woolly lemurs. Indris have only a stump of a tail and silky fur, while other indriids have long tails. Woolly lemurs have thick, woolly fur and small ears almost concealed in the fur of their head. Sifakas have long, thick fur dorsally which becomes sparse on their underside. They lack fur on the face. Pelage color varies considerably among species, from striking black and whites to browns and yellows. Their faces are somewhat shorter than lemurs and the legs are about 1/3 longer than the arms. The last 4 digits of the feet are joined together with flaps of skin and they act as a single unit in opposing the first toe. Females have a single pair of mammae, a baculum is present in males, and the dental formula is: I 2/2, C 1/0, PM 2/2, M 3/3. Sometimes the dental formula is interpreted as: I 2/1, C 1/1, PM 2/2, M 3/3. The lower toothcomb is made up of 4 teeth, rather than 6 as in lemurs. There is no recognized sexual dimorphism. (Nowak, 1991)

A captive Propithecus coquereli lived for 30.5 years. Other Propithecus species have lived for more than 20 years in captivity. (de Magalhães, 2008; Nowak, 1991)

Indriids generally live in small groups made up of one or several females, one or several males, and dependent young. Groups are generally territorial and, although females and young are most frequently dominant over males, males are responsible for territorial defense. Group life is generally described as peaceful, except during the breeding season in some species, where male-male aggression becomes common. (Mittermeier et al., 2006; Nowak, 1991)

Indris and sifakas are diurnal, while avahis are nocturnal. Indriid species are fairly sedentary, with groups moving 300 to 1100 meters per day. Home ranges often overlap and are from to 1 to 18 hectares in size. (Mittermeier et al., 2006; Nowak, 1991)

Indriid species are all characterized as "vertical clingers and leapers." Indriids typically hold themselves vertically in trees and are capable of impressive leaps of up to 10 meters. They may also suspend themselves during feeding. Also unique to this group is bipedal leaping on the ground, especially in indris and sifakas, in which they jump on their two rear feet while holding the arms above their heads or in front of their bodies. (Mittermeier et al., 2006; Nowak, 1991)

Like other primates, indriids rely heavily on vision for finding food, navigating, and in communication. Indriids have excellent, binocular vision. Woolly lemurs are nocturnal and have excellent vision in low light. Vocalizations play an important role in social communication as well. Indris sing melodious songs that can be heard up to 2 km away. Members of groups often sing together. It is thought that vocalizations serve to advertise territories, maintain contact between group members, and convey information on age, sex, and reproductive condition of individuals. Avahis and sifakas also use vocalizations extensively in territorial advertisement and distance communication. In fact, the name "sifaka" comes from the explosive sound they make in response to threats, sounding like "see-fak." The sound is accompanied by a rapid jerk of the head and is often given several times in quick succession. Scent marking has been reported in sifakas. (Mittermeier et al., 2006; Nowak, 1991)

All indriids are vegetarians, eating leaves, buds, fruit, bark, and flowers. They occupy a plant-eating primate niche that is occupied by howler monkeys in the neotropics and and leaf-eating monkeys in Africa and Asia. Their salivary glands are enlarged, as in African and Asian leaf-eating monkeys. (Mittermeier et al., 2006; Nowak, 1991; Tattersal, 1982)

The only native predator of lemuroids in Madagascar are fossas (Cryptoprocta ferox). Humans also hunt indriids. (Mittermeier et al., 2006; Nowak, 1991)

Indriids are important folivores in their native ecosystems, impacting plant communities. (Nowak, 1991)

There are no known negative effects of indriids on humans.

Indriids are important members of their native ecosystems. The unique nature of indriids means they are the focus of ecotourism activities that benefit local people. Indriids are also kept in zoos and are the focus of research on evolution. (Nowak, 1991)

All Malagasy primates are threatened, primarily by habitat destruction. Indriids are protected by law in Madagascar, but habitat destruction continues. Indris are also protected by local custom. (Mittermeier et al., 2006; Nowak, 1991)